Extracorporeal circuits, and the use of a filtration device in such a circuit, are well known and are commonly used therapeutically or clinically to prevent or reduce damage caused by leucocyte activation as a result of leucocyte contact with foreign matter, as well as a number of other diseases and conditions.
Leucocytes are a type of blood cell in the immune system which constitute the principal means of defense against antigens, such as infection by pathogenic microorganisms and viruses, and probably also against most cells that undergo transformation into cancer cells. Leucocyte activation, the leucocytic monitoring and arming functions, proceeds from a complex series of biochemical interactions, typically terminating in engulfing and digesting the antigen. If the leucocytes have been so activated, but lack an appropriate antigenic target, the leucocytes may inflict damage to internal organs, particularly ischemic tissues, i.e., tissues in which no blood is flowing such as the heart and lungs during certain surgical procedures.
Moreover, with increasing frequency, the most common leucocyte, the granulocytic neutrophil, has been implicated as the mediator of tissue destructive events in a variety of disorders, including reperfusion injury, respiratory distress syndromes, rheumatoid arthritis, skin disorders and ulcerative colitis. The commonality which pervades these pathologies is the neutrophil's ability to release a number of agents which can disrupt and destroy normal cellular function, dissolve connective tissue, and cause injury to organs.
It has also been shown that circulating leucocytes contribute to or mediate ischemic and reperfusion injury during organ preservation, particularly following extended preservation of the heart-lung bloc commonly required during cardiopulmonary bypass operations (CPB). Leucocytes have also been associated with increased oxygen radical activity, pulmonary edema, and vasoconstriction.